Presently, vaporization of water in an electric warmer is needed in so-called vaporizers, i.e. in sterilizers, for instance for baby bottles. The power supply in such devices is most of the time monitored and controlled via temperature monitoring, as is e.g. shown in U.S. Pat. No. 4,716,278. In this process, however, heating power may unnecessarily be supplied if heating is continued when the whole amount of water has already evaporated.
A further known arrangement of a sterilizer is shown in U.S. Pat. No. 3,347,618. In this sterilizer, the heating power is switched off directly after vaporization of the whole water reservoir for the reason that heating is carried out via open electrodes and current flows directly through the filled-in water. This solution, however, has significant drawbacks in terms of safety.
Furthermore, such electric warmers are often used for heating baby food contained in a container. Apart from heating baby food in a water bath, it is also known that baby food is heated by means of water vapor as the heat transfer medium. An electric baby food warmer with water vapor is e.g. known from DE 102 14 905 C1. The advantage of this solution is that only a very small amount of water must be evaporated and that due to the high temperature and the evaporation enthalpy of the water vapor the baby food can be heated rapidly while saving energy. After the heating power supply has been interrupted, the small amount of water cools relatively rapidly, thereby falling below the boiling point, and heat is no longer transferred to the food container. As a result, an overheating of the baby food to be heated can be avoided. In the known baby food warmers of the above-indicated type, power control is however carried out via a timer which switches off the power supply after an adjustable heating time has been reached. The timer has the function to ensure a defined temperature of the food to be heated, also in the case of varying food amounts and food temperatures, but always requires the same amount of liquid for a perfect function. This is difficult in the case of comparatively small volumes because small amounts of water (e.g. 10 ml to 20 ml) can most of the time not be filled with adequate accuracy with the measuring methods that are standard in the household sector. Therefore, such a timer provides a power control solution which can be handled particularly easily and at low costs.
If, as an alternative, a thermostat is used for controlling the heating power supply in said warmers, this has the drawback that control and temperature measurement are very complicated.